The objectives of the proposed research include (1) a determination of the role of viral-modified endoplasmic reticulum in the morphogenesis of virions, (2) a determination of the role that S14 particles and S73 empty capsids play in the morphogenesis of poliovirions, and (3) the production of poliovirions from precursor particles and viral RNA in vitro by means which mimic the maturation process in vivo. The chemical nature of the assembly activity associated with rough membranes that convert S14 particles into empty capsids will be studied by determining the effect of enzymes and substances that react specifically with glycoproteins. In addition, attempts will be made to dissociate the assembly activity from membranes and/or to "solubilize" the assembly factor(s) in order to make possible their further purification by conventional methods. Experiments will be performed to elucidate the mechanism of action of the assembly activity.